Various types of dispensers exist for dispensing heated liquids at specified application temperatures. In many instances the dispenser must discharge the liquid within a precise, elevated temperature range. One such application is the dispensing of hot melt adhesives. Many hot melt adhesive dispensers take the form of a gun or module having a nozzle and an internal valve for regulating liquid flow through the nozzle. Often, the nozzle includes a valve seat engageable by a valve stem for flow control purposes. The dispenser module is typically heated to a desired liquid application temperature such as by being directly connected to a heated manifold. The temperature of the nozzle should be maintained at the required liquid application temperature so that the liquid will perform satisfactorily. If the nozzle is too cool, the liquid may cool down too much just prior to discharge, thereby adversely affecting the liquid cut-off at the nozzle when the valve stem is closed. More specifically, liquid hot melt adhesive may not shear properly when the valve is closed and instead may string and produce so-called angel hair. This angel hair can become airborne and contact other equipment or machinery, or adversely affect the substrate in other areas. Furthermore, if hot melt adhesive exits the nozzle at a reduced temperature, the reduced temperature can compromise the adhesive bond.
A prior two-piece nozzle incorporates an outer nozzle portion formed of a heat conductive metal, such as brass. As brass and other heat conductive metals are relatively soft, however, a carbide steel or other wear-resistant, press-fit insert is typically used as the valve seat portion of the nozzle. This two-piece nozzle sufficiently transfers heat from the dispenser body to the outer nozzle portion; however, it is a relatively costly construction.
A less costly one-piece nozzle with an integral valve seat unit has been manufactured entirely from stainless steel. However, because stainless steel has relatively low thermal conductivity properties, heat does not readily transfer from the dispenser body to the nozzle. Therefore, in some situations, this nozzle may be unable to maintain the requisite liquid temperature at the nozzle outlet.
To solve problems such as those mentioned above, it would be desirable to provide a relatively low cost nozzle having high wear resistance and high thermal conductivity properties.